Although it is recognized that biotin status is compromised during human pregnancy (particularly during the third trimester), no human dietary studies have been conducted to assess dose-response relationships, maternal-fetal compartmentation, or dietary biotin requirements. Consequently, the Food and Nutrition Board of the Institute of Medicine were not able to establish a recommended dietary allowance (RDA) for biotin. Instead an adequate intake (AI) level of 30 mcg biotin per day for adults was estimated without upward adjustments for pregnant women. Goal: The goal of this study is to provide data that will scientifically inform the development of a biotin RDA for pregnant women Specific Aims: The specific aims of this proposal are to: i) test the hypothesis that dietary biotin requirements are increased during pregnancy; ii) test the hypothesis that maternal and fetal biomarkers of biotin status are positively correlated; and iii) investigate the dose-response relationship between dietary biotin intake and validated biomarkers of biotin status. Procedure: To accomplish these aims, a 12-week controlled feeding study conducted in pregnant women (n=10, 21-40y, 27 wk) and nonpregnant control women (n=10, 21-40 y) will be extended to enable a dose response assessment of biotin in these women. Quantitation of the biotin content of the diet will be performed along with measurements of maternal/fetal biomarkers of biotin status including those linked to biotin deficiency (i.e. 3-hydroxyisovaleric acid) and biotin catabolism (i.e. bisnorbiotin and biotin sulfoxide). Expected Outcomes: This study will be able to delineate the relationship between maternal and fetal biotin status in humans; provide insight into the factors that may contribute to the suboptimal biotin status observed during pregnancy; and facilitate an estimation of the level of maternal dietary biotin intake required to meet the increased demands during pregnancy and ensure an adequate supply of biotin to the developing fetus. Collectively, these data are expected to scientifically inform the development of a biotin RDA for pregnant women that is designed to improve maternal and fetal health.